• r10 sl Stack limit
• r11 fp Argument pointer
• r12 ip Temporary workspace. Register r12 (IP) may be used by a linker as a scratch register between a routine and any subroutine it calls (for details, see §5.3.1.1, Use of IP by the linker). It can also be used within a routine to hold intermediate values between subroutine calls.
• r13 sp Stack pointer
• r14 lr Link register Workspace

Special-purpose program status registers (xPSR)

• APSR Application PSR contains the condition code flags. Before entering an exception, the processor saves the condition code flags on the stack
• IPSR Interrupt PSR contains the Interrupt Service Routine (ISR) number of the current exception activation.
• EPSR Execution PSR contains the Thumb state bit (T-bit).